Poloxamers are non-ionic block copolymers of ethylene oxide (EO) and propylene oxide (PO). They are used in pharmaceutical formulations as surfactants, emulsifying agents, solubilisation agents and dispersing agents.
A well known analytical approach for characterising a poloxamer is a calorimetric method in which the UV absorbance at 320 and 620 nm, resulting from complex formation of the poloxamer with cobalt (II) thiocyanate, is analysed.
Yun Mao et al (Journal of Pharmaceutical and Biomedical Analysis, 35 (2004), 1127) describe for poloxamer determination the use of size exclusion chromatography (SEC) using a column with THF as mobile phase and refractive index (RI) detection. The method was applied to the pharmaceutical formulations Avapro, Neurontin and Sudafed wherein the active principle is a “small molecule”. Small molecules are conveniently separable by SEC from the high molecular mass poloxamers.
Size-exclusion chromatography (SEC), also called gel-permeation chromatography (GPC), uses porous particles to separate molecules of different sizes. It is generally used to separate polymer molecules and to determine molecular weights and molecular weight distributions of polymers. Molecules that are smaller than the pore size can enter the particles and therefore have a longer path and longer transit time than larger molecules that cannot enter the particles. All molecules larger than the pore size are unretained and elute together. Molecules that can enter the pores will have an average residence time in the particles that depends on the molecules size and shape. Different molecules therefore have different total transit times through the column.
No method has been provided so far allowing the quantitative determination of poloxamers in protein samples, wherein the protein has a molecular mass which is comparable to the poloxamers.
There is in particular a need for the quantitative determination of poloxamers in protein samples, wherein the protein has a molecular mass between 5 to 70 kDa, preferably between 20 to 70 kDa.